Signaling system



86 J. E. KEYSTON ETAL 2,241,204

SIGNALING SYSTEM Filed April 17, 1936 Mme/flora John Edgar Keys/onLeonard F. Broadway Patented May 6, 1941 UNITED STATES PATENT. OFFICEJohn Edgar Keyston, Hayes, and Leonard Francis Broadway, Hillingdon,England, assignors to Electric & Musical Industries Limited, Hayes,Middlesex, England, a company of Great Britain Application April 1'7,1936, Serial No. 74,826

. In Great Britain April 17, 1935 a 1 i (Cl. 178-72) I l'Claim.

The present invention relates to cathode ray tube circuit arrangementsfor television and like purposes.

Cathode ray tubes are known in which an image of an object to betransmitted, such as a frame of a motion picture film, is projected onto a mosaic screen, the screen being scanned by a cathode ray from asuitable gun for the purpose of generating picture signals.

The mosaic screen may be constituted by a plurality of small, discretephoto-electric elements each having capacity to a common signal plate,or by a plurality of mutually insulated conducting elements, one side ofthe screen being made photo-electric and has an optical image of theobject to be transmitted projected upon it, while the other side isarranged to be scanned by the cathode ray. Furthermore, the mosaicscreen may comprise a plurality of mutually insulated conductingelements which are not photoelectrically active; in this case, anelectron image may be focused on to the mosaic screen, by any suitableelectron-focusing means, from a photo-electric surface on which anoptical image of the object to be transmitted is projected. Theinvention is also applicable when the mosaic screen in thelast-mentioned case takes the form, for example, of a sheet of mica, orother material which has a high resistance in the plane of the surfaceon which the electron image is focused.

It has been proposed in a television system utilising a transmittingtube embodying a mosaic screen to modulate the intensity of the ray atthe frequency of a transmission carrier; for this purpose, carrierfrequency oscillations have been fed to a control electrode forming partof the gun, the output of the device then taking the form of a carrierwave modulated by the picture signals. It has further been proposed tofeed synchronising signals to the control electrode referred to above,in addition to the carrier oscillations.

It is an object of the present invention to provide a cathode ray tubecircuit arrangement in which improved means are provided for effectingmodulation of the electron beam.

According to the present invention, in a circuit arrangement embodying acathode ray tube comprising a cathode, a screen, means for focusingelectrons from said cathode in a narrow beam upon said screen, and twoelectrically separate electrodes arranged in succession along the pathof the ray between said cathode and said screen, there are providedmeans for enabling modulating potentials of diiferent characters to beapplied to saidtwo electrodes respectively.

In a preferred form of the present invention, a circuit arrangementcomprises a cathode ray tube of the double acceleration type, that is, atube in which electrons from the cathode undergo at least twoaccelerations during their passage from the cathode to the screen, andare subjected between two of said accelerations to a deceleration. Sucha tube may comprise a cathode and a screen, such as a mosaic screen,and, arranged between the cathode and the screen in the following order,a cathode screen, an accelerator electrode, a modulator electrode andone or more anodes; in operation, the accelerator and the anode oranodes are maintained at suitable positive potentials relative to thecathode and serve to accelerate electrons from the cathode, the cathodescreen and the modulator'electrode are maintained at negative potentialsrelative to the cathode, so that the modulator serves as a decelerator,and modulating potentials of different characters are applied betweenthe cathode screen and the cathode, and between the modulator electrodeand the cathode respectively.

When such a tube is employed in a television transmission system, animage of the object to be transmitted is projected on to the mosaicscreen, and the electron beam is deflected by electrostatic orelectromagnetic means, in known manner, so as to scan the screen. Insuch an arrangement, according to one aspect of the present invention,oscillations at a carrier frequency are applied between the modulatorand the cathode, and synchronising ignals are applied between thecathode screen and the cathode, the output of the tube then being in theform of a carrier oscillation modulated both by picture signals and bysynchronising signals.

The synchronising signals may be arranged to reduce the intensity of theelectron beam to zero, so that the synchronising signals are representedin the modulated carrier by intervals of zero carrier amplitude.

The application of the carrier oscillations and the synchronisingsignals to different control electrodes has the important advantage overthe known arrangement referred to that it can readily be arranged thatthere is substantially no coupling between the carrier source and thesource of synchronising signals, and interaction between these sourcescan thus be avoided.

In some cases, it may be desired to maintain the level of thetransmitted picture signal substantially constant; for this purpose,there may The invention will be further described with I reference tothe accompanying drawing which shows, by way of example, a circuitarrangement according to the invention" embodying a transmitting cathoderay tube.

Referring to the drawing, the tube I has a cathode 2, a mosaic screen 3,and, arranged" beamplitude. Any known or suitable means may be providedfor varying the amplitude of the cartween the cathode and thescreen-,in' the: order a named, the following electrodes a cathodescreen4, an accelerator 5, a modulator 6 and first and tifier. H and thecathode-of'tube l is con-nected to the join of resistances I5 and- IB.The accelerator 5 and the first and second anodes 5' and T are connectedto points at progressivelyi'n creasing. positive potentials in thepotential divider, and the cathode screen d is'given-a negative biasrelative to the cathode 2 by connection to an adjustable tapping point.in resistance t6; the modulator 6 derivesa negativebias fromanadjustable tapping point in a resistance H connected in shunt withresistance It. Carrier frequency oscillations are fed tomodul'ator 6from source I8 throughtrans-former' l9, and synchronising impulses fromsource 20- are taken off from resistance 21 and appliedtocathode screen4'. p

The synchronising signals are preferably fed to the cathode screen 4 inthenegative sense; and at such a level that they reduce the intensity ofthe cathode-ray to-zere, so that, in the signals set up acrossresistance l0; the synchronising signals are represented by periods ofzero carrier rier oscillation applied to modulator 6.

The invention is not limited to the arrangement described by way ofexample above, and many modifications of the invention, within the scopeof the appendedclaim, will occur to those versed in the" art;

We claim:

A television signaling system comprising a cathode ray imagetransmitting scanning tube, said tube having included therein meansincluding an electron source to develop a cathode ray beam and aphotoelectrically responsive mosaic electrode:- adapted? to receive alight image of which an electro-optical replica is to be produced atreceiving: points and a signal plate element associated with the mosaicelectrode, a signaling circuit connected with the signal plateelectrode, means comprising a plurality of electrode elements: toaccelerate and focus the developed cathode ray: beami upon the mosaicelectrode, means to deflect the cathode ray beam in a predeterminedtraversal pattern relative to the mosaic electrode to: release energy tothe signal circuit which is proportional. tothe brilliance of theoptical image cast upon the mosaic, a source of" synchronizing signalenergy, a. plurality of modulating electrodes intermediate the electronscurceand the mosaic and along the path of the electron beam, one ofsaid modulating elec trodes being located nearer the electron sourcethan oneof theaccelerating electrodes and the other of the modulatingelectrodes being located nearer the mosaicthan the said acceleratingelectrode, anelectrical connection to supply the generated carrier toone of the-modulating electrodes sothat the signal impulses in thesignaling circuit are modulations ofthe said carrier frequency, anelectrical connection to supply the synchronizing signals to the otherof the modulating electrodes to suppress the cathode raybeam atpredetermined intervals, said independent connections tothe modulatinelectrodes being' suchthat direct interaction between thecarrier'frequencyenergy sourceand the synchronizing signal energy sourceis'reduced' toa minimum value;

J OHN' EDGAR; KEYSTON. LEONARD FRANCIS BROADWAY;

